This invention relates to a novel lubricating grease composition having improved salt water corrosion resistance. More particularly, this invention involves a lubricating grease composition comprising a lithium complex grease thickener, a metal naphthenate and a quaternary ammonium salt.
Greases thickened with lithium soaps are well known in the prior art and such greases have found wide acceptance in a variety of applications. Generally however, these greases cannot be effectively used in marine applications due to the relatively low resistance to salt water and brackish water corrosion.
It is well known that rust inhibitors and various other additives can be incorporated into grease compositions to provide or improve the properties of such greases. For example, U.S. Pat. No. 3,271,309 issued Sept. 6, 1966 to G. P. Carusso discloses an oleophilic, ammonium modified, clay thickened grease containing a metal carbonate and optionally a molybdenum or antimony sulfide and lead naphthenate to improve the extreme pressure properties. U.S. Pat. No. 3,623,982 issued Nov. 30, 1971 to W. P. Scott discloses conventional calcium base greases containing a combination of lead naphthenate, a dialkyl dimethyl quaternary ammonium nitrite or nitrate and optionally a fatty imidazoline alkyl diamine dicaprylate as a rust inhibiting package. While the patent indicates the general suitability of the so modified calcium base greases in marine applications involving a salt water environment, it specifically notes that such a rust inhibiting additive combination is not effective in preventing salt water corrosion when added to lithium base greases.
U.S. Pat. No. 3,730,896 issued May 1, 1973 to W. P. Scott et al discloses a low temperature grease composition having effective rust inhibiting properties and comprising a major proportion of a synthetic hydrocarbon lubricant, such as a monoalkylated benzene, a grease-forming amount of a lithium soap of a fatty acid and a rust inhibiting amount of lead naphthenate, didodecyl dimethyl quaternary ammonium nitrite or nitrate and a fatty imidazoline alkyl diamine dicaprylate. As noted in the patent, this particular rust inhibitor combination while effective in providing salt water rust protection in a lithium soap-synthetic hydrocarbon lubricant grease, was not effective in a conventional lithium soap-petroleum oil grease.
U.S. Pat. No. 3,940,339 issued Feb. 24, 1976 to G. A. Clarke et al discloses a lubricating grease having an exceptional ability to protect metal bearing surfaces against rusting or corrosion in the presence of salt water and comprises a lithium complex grease thickener made up of a lithium soap of C.sub.12 to C.sub.24 hydroxy fatty acid and boric acid and a corrosion inhibiting combination of a dialkyl dimethyl ammonium nitrite and an amino imidazoline. While this grease composition did provide excellent salt water corrosion resistance, it was not particularly suitable in applications involving the use of rubber seals since it often caused embrittlement of the rubber.